The present invention relates to techniques for discriminating sharp edge transitions produced during the optical scanning of differently reflective regions as, for example, in the CCD or similar camera or sensor scanning of conductors on printed circuit boards and other applications similarly involving differently reflective regions of a surface.
Considering, for illustrative purposes, the abovementioned application of CCD scanning of printed circuit boards, the scanning signal processing from the CCD must umambiguously detect the transition between, for example, copper lines and background of resist in order to enable the inspection of the integrity of the lines. Spurious reflection variations, however, as from tarnish spots or the like on the copper often provide false indications. It is to the problem of improving and, indeed, enabling the discriminating of sharp edge transitions between the differently reflective regions of the board, represented in this example by the transition between the copper and the background, with insensitivity to or irrespective of the presence of subsequent spurious reflection variations in these regions such as those caused by tarnish or the like, that the present invention is principally directed.